Incidence

Fractures of the humeral shaft account for 1% of all fractures. Most of these fractures can be treated conservatively by functional bracing with satisfactory outcomes. The humerus is a non-weight bearing bone and shortening up to 3 cm is well tolerated while malalignment up to 20° in the AP plane and 30° in varus and valgus can be compensated by the shoulder and elbow joints.

Current methods of treatment

Surgical treatment must be considered in these circumstances:

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  When the alignment is unacceptable

  
  
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  In open fractures

  
  
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  In humeral shaft fractures associated with articular injuries

  
  
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  When there is vascular injury

  
  
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  In radial nerve lesions associated with spiral fractures of the distal third of the diaphysis (Holstein-Lewis type)

  
  
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  When a radial nerve palsy appears after fracture reduction

  
  
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  In cases with a floating elbow

  
  
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  Pathological fractures

  
  
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  Bilateral humeral shaft fractures

  
  
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  In the polytrauma patient

There are several methods of fixation available, namely, open reduction and internal fixation by plate, intramedullary nailing, and external fixation. The selection of fixation method is based on the condition of the soft tissues, fracture location, pattern of fracture, bone quality, canal diameter, available facilities and resources, and the skills and experience of the surgical team. While external fixation is reserved mainly for open fractures or closed injuries with severe soft-tissue compromise, both plating and intramedullary nailing can be used for most humeral shaft fractures. Locked intramedullary nailing can be performed through relatively small incisions and therefore result in less soft-tissue trauma. Plate fixation, on the other hand, requires extensive exposure and soft-tissue dissection, but has one major advantage over nailing—it can provide very stable fixation. In order to make use of the advantages of plate fixation while avoiding the disadvantages of open plating, such as excessive soft-tissue stripping and devascularization, the plate may be introduced using minimally invasive plate osteosynthesis (MIPO) techniques. The challenge with MIPO when used for humeral shaft fractures is the presence of major nerves and vessels that, if injured, can lead to serious consequences. The most common structure at risk is the radial nerve. Anatomical studies have shown that there is a “safe zone” in the humerus that is not crossed by any major nerve or vessel. This zone is suitable for MIPO techniques [ 1] and lies on the anterior surface of the humeral shaft deep to the brachialis muscle.

Indications and contraindications for MIPO

Minimally invasive plate osteosynthesis can be performed using an anterior approach for most closed humeral shaft fractures. It is possible to treat fractures that extend from 5 cm distal to the bicipital groove to 5 cm proximal to the coronoid fossa. The plate must be fixed with two or three screws in each fragment and it works like a flexible extra-medullary splint stimulating callus formation.

Good indications for MIPO of the humeral shaft include:

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  Comminuted shaft fractures

  
  
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  Fractures extending to the proximal or distal shaft

  
  
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  Segmental fractures

  
  
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  Small medullary canals (< 8 mm)

  
  
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  Deformed shaft caused by malunions

  
  
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  Open growth plates

  
  
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  Polytraumatized patients, especially those who need multiple simultaneous procedures

  
  
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  Fractures with neurovascular injuries needing repair

Contraindications to MIPO include:

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  Severe soft-tissue loss without coverage of exposed bone

  
  
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  Osteomyelitis

  
  
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  Delayed surgery with significant shortening

  
  
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  Delayed reconstructions (eg, requiring open bone graft)

  
  
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  Brachial plexus lesion, and other kinds of flaccid palsy of the upper arm; the lack of muscle action retards or prevents callus formation when relative stability constructs are used

The presence of a radial nerve injury in a humeral shaft fracture is not an absolute contraindication to MIPO technique. If considering MIPO it is recommended to explore the radial nerve first and then fix the fracture using a MIPO technique. For example, such a procedure could be performed in distal spiral fractures (Holstein-Lewis type) with a radial nerve palsy.

Bone

The humeral shaft extends from the inferior border of the pectoralis major insertion proximally to the supracondylar ridge distally. This region encompasses the middle 3/5 of the entire humerus. Cross-sectional shape varies from round proximally to triangular distally ( Fig 13.1-1 ). The anterior aspect of the humerus possesses an anterior ridge with anterolateral and anteromedial surfaces. The posterior aspect of the humerus presents a broad, flat surface extending from the posterior aspect of the neck of the humerus to the olecranon fossa distally. The deltoid tubercle forms a lateral prominence just proximal to the midshaft. Knowledge of the anatomy of the humerus is essential when contouring the plate to fit the bone surface.

Muscles

The arm has two major muscle compartments, flexor and extensor, which are separated by the medial and lateral intermuscular septi. The flexor or anterior compartment contains three muscles: coracobrachialis, biceps brachii, and brachialis. All are supplied by the musculocutaneous nerve except the lateral part of the brachialis, which is supplied by the radial nerve. The extensor or posterior compartment has only one muscle, the triceps brachii, which is supplied by the radial nerve.

Nerves

The radial nerve is a continuation of the posterior cord of the brachial plexus. It runs along the posterior wall of the axilla, and then passes through the triangular space formed by the long head of the triceps, shaft of the humerus, and teres major muscle. The nerve crosses from medial to lateral by lying in the spiral groove close to the bone on the posterior aspect of the midshaft of the humerus. After crossing the posterior surface of the humerus, the radial nerve pierces the lateral intermuscular septum to enter the anterior compartment where it lies between the brachialis and brachioradialis. In this area the radial nerve is separated from the bone by the brachialis muscle.

The median nerve lies in the anterior compartment and runs alongside the brachial artery on the anteromedial aspect of the arm. In the upper arm, the ulnar nerve lies posterior to the brachial artery in the anterior compartment. After running down 2/3 of the arm, it pierces the medial intermuscular septum to enter the posterior compartment and then continues distally to the posterior aspect of the medial epicondyle. The musculocutaneous nerve is a branch of the lateral cord. The nerve enters the coracobrachialis about 5–8 cm distal to the coracoid process on its medial side. After piercing the coracobrachialis, it runs on the anterior surface of the brachialis and branches to supply the biceps and medial part of the brachialis muscle. The nerve continues distally to supply sensation to the lateral forearm (lateral cutaneous nerve of the forearm).

The safe zone of the humerus

To identify the safe zone of the humerus, it is necessary to understand the cross-sectional anatomy of the proximal, middle, and distal humerus ( Fig 13.1-1 ).

In the proximal humerus, the axillary vessels and three nerves (radial, median, and ulnar nerves) run along its medial side. The branches of the axillary nerve and posterior humeral circumflex vessels are posterior and continue laterally.

In the proximal humeral shaft the only safe zone that has no neurovascular structures overlying it is the anterior aspect ( Fig 13.1-1a ).

The profunda brachii vessels and the radial nerve run close to the posterior aspect of the midshaft of the humerus in the spiral groove. The brachial artery and vein along with the median and ulnar nerves are on the medial side of the humerus. The musculocutaneous nerve lies on the anterior surface of the brachialis muscle. The safe zone of the midshaft of the humerus is therefore its anterior surface deep to the brachialis muscle ( Fig 13.1-1b–c ).

In the distal arm the radial nerve moves laterally, and, after piercing the lateral intermuscular septum, lies between the brachialis and the brachioradialis muscles lateral to the humerus.

The brachial vessels, median nerve and ulnar nerve are on its medial side. The musculocutaneous nerve lies anterior to the brachialis muscle. The safe zones of the distal shaft of the humerus include its posterior surface as well as its anterior surface deep to the brachialis muscle ( Fig 13.1-1d–e ).

From these cross-sectional studies, it is evident that the safe zone for the percutaneous insertion of a straight plate for the humeral shaft is on its anterior surface deep to the brachialis muscle ( Fig 13.1-2 ).